The invention relates to a solid bowl centrifuge, particularly for separating agents of different density or mixtures thereof and/or suspensions that are difficult to separate into a comparatively lighter and at least one heavier phase.
More particularly, the invention relates to a method and apparatus including a drum seated rotatably on a shaft and forming a settling sump therein and elements for the admission of the agents to be separated and for discharging the separated phases. Centrifuges of this type are disclosed, for example, by German published application No. 33 17 047 wherein a displacement member extending in the direction of the rotational axis and seated rotatably with a hollow shaft is arranged along the settling sump at a distance from the inside wall of the drum, and the centrifuge is constructed with means for operation in cocurrent flow, whereby the admission element for the medium to be separated is arranged at the intake region of the settling sump and the discharge elements for the separated phases are arranged departing from the outlet region thereof.
Although the technical field involving centrifuges represents a technology that has been known, the increasing utilization of microbiology for processing waste water and/or liquid manure, for example, makes constantly increasing demands of the separating capability of centrifuges, since the gel-like sludge that thereby arises resists sedimentation and thus presents great difficulties in the phase separation.
Different methods and apparatus have been disclosed for dewatering such predominantly viscous sludges, but these have not yet been capable of resolving the problem in a satisfactory manner.
For example, German utility model No. 84 60 004.7 proposes an overflow separation centrifuge for separating treatment of sludge that comprises a liquid discharge pipe that projects into the drum and has a peeling spout at its free end, with the peeling spout being adjustable for skimming a phase in differing depth of the sedimentation pond. Such an apparatus is extremely difficult to operate and is also susceptible to malfunction.
Another centrifuge disclosed by German publication application No. 26 51 657 has a purified liquid overflow at a location between admission and solids discharge, whereby the overflow element is composed of a plurality of small pipes projecting radially into the clarifying chamber from the outside toward the inside. The height of damming can thereby be set in that the small pipes are allowed to project into the clarifying chamber to a greater or lesser distance.
Disadvantageously, energy is lost in this structure with the peripherally discharged purified phase and the liquid that has been centrifuged out produces an extremely undesirable frothing. Foam-inhibiting agents must be utilized on a case-by-case basis for combatting this and these incur costs and also contaminate the purified phase. This known apparatus also does not prove satisfactory in resolving the stated problem.
German published application No. 33 17 047 has proposed a solid bowl worm centrifuge for this purpose having a cylindrical structure for parting suspensions that are difficult to separate. This worm centrifuge has a parting disk at the end of the separating chamber and includes purified phase channels arranged preceding the parting disk and sediment channels arranged following the parting disk. Both discharges lead out of the centrifuge drum in the region of the center of said centrifuge drum. A measuring cell for identifying the content of dry matter is arranged in the sediment discharge and controls a quantity regulating element in the purified phase discharge conduit based on the measure of the constant solids content in the sediment.
The known apparatus requires delivery of the suspension with pressure between 0.4 through 0.6 MPa and thus requires a sealing of the bearings.
Such seals are extremely complex in structure. They are also difficult to maintain, are extremely susceptible to wear and, thus, susceptible to malfunction. This known centrifuge also is not technologically satisfactory.
An object of the invention is to provide a centrifuge of the species referred to wherein the phase separating of agents that are difficult to separate, for example, sewage treatment sludges, is possible while largely avoiding energy losses and without a complicated structure of the centrifuge.
Another object is to provide a centrifuge which avoids pressurized operation and employs a simple control of the solids contents in different phases that contain solids, and which can be erected with optimally little outlay for manufacturing, assembly and maintenance costs and can be operated with an economical energy expenditure.